Degreasers and defluxers are commonly used for degreasing, precision cleaning and defluxing of various articles, such as removing solder or flux from printed circuit boards. The articles are typically conveyed through one or more solvent zones within the degreaser/defluxer for contact with a solvent, such as fluorocarbon based CFC-113, manufactured by Genesol/Baron-Blakeslee, Melrose Park, Ill., a division of Allied-Signal Incorporated, assignee of the present invention. The articles are cleaned by entering the degreaser/defluxer on a conveyor through an entrance end thereof for passage through a solvent vapor zone, immersion within liquid solvent, solvent spraying, or any combination thereof. The articles are then conveyed from the degreaser/defluxer through an exit end.
Parts may also be degreased or defluxed by the use of open top degreasers or defluxers of a type disclosed in U.S. Pat. No. 4,261,111 to Rand, issued April, 1981. An open top degreaser or defluxer generally comprises a tank having side walls forming a rinse and/or boil sump at the tank bottom where solvent is heated to form a vapor zone thereabove. Condensing coils define the upper limit (i.e., vapor line) of the vapor zone with an overhead freeboard region extending to the open top. Parts to be cleaned are submerged into the sump and/or the vapor zone through the open top and are similarly removed.
The entrance and exit ends of conventional conveyorized degreaser/defluxer equipment, and the open top of the open top degreasing/defluxing equipment, are generally in open communication with the ambient environment and the solvent within the equipment. Consequently, there is a loss of solvent to the surrounding environment caused by diffusion of solvent vapor into the air. This problem is exacerbated by air drafts entering the equipment through the entrance and/or exit ends and creating turbulence therewithin.
Solvent vapor loss also occurs by evaporation of the solvent as the solvent covered articles exit the equipment. The evaporation problem may be as significant as the solvent diffusion problem depending upon the geometry and number of parts being cleaned.
The use of CFC-113 and Freon type solvents and vapor emission thereof into the environment also contributes to undesirable stratospheric ozone depletion. Consequently, it is expected that new HCFC solvents, which effect the environment significantly less than the CFC-113 and Freon type solvents, will replace the latter in accordance with environmentally safe operating principles. However, since these new HCFC solvents boil at much lower temperatures (e.g. 82.degree. F.-86.degree. F.) than the above solvents (103.degree. F.-118.degree. F.) currently being used, solvent loss is likely to increase, particularly as a result of evaporation of liquid solvent coating the articles as the articles are conveyed from the degreaser or defluxer equipment through the exit end thereof, or removed through an open top of an open top degreaser/defluxer.
In the aforementioned co-pending application, the problem of preventing solvent vapor loss by minimizing solvent evaporation as the solvent covered articles exit the equipment is addressed through the application of heat by placement of heating coil means within the vapor zone located in the exit end and passing the articles in proximity of the heating coil means to evaporate the liquid solvent therefrom. More specifically, the heating coils utilize waste heat from a compression-expansion type refrigeration system which conventionally supplies chilled refrigerant to one or more condensing coils maintaining the vapor line within the degreaser/defluxer to reduce solvent emissions. These condensing coils typically serve as expansion coils within the refrigeration system and are situated in a known manner in various locations within the vessel and entrance/exit ends thereof. The refrigeration system conventionally includes a compressor section and an evaporator section. The compressor section has a compressor which compresses a refrigerant gas received from the condensing coils (evaporator section) into a hot refrigerant gas which is directed to the heating coils functioning as a condenser within the compressor section. After releasing the heat to dry the parts, as aforesaid, the refrigerant is then directed through an expansion valve into the condensing coils.
As a result of extensive experimentation, it was discovered that the heat from the aforementioned heating coils may not fully dry the parts if liquid solvent or solvent droplets were trapped under or within the parts, usually as a result of the parts having a complex surface geometry. It is theorized by the present inventors that the inability to sufficiently dry the parts stems from trying to heat and thereby evaporate the liquid solvent (coating or trapped within the parts) within the vapor zone. Within the vapor zone, the vapor temperature is constant and in steady state. To raise the vapor temperature it is necessary to superheat the vapor. Furthermore, the solvent vapor itself within the vapor zone is an excellent insulator which prevents heat from the heating coils from radiating towards the parts, unless the heating coils are brought extremely close to the parts to overcome the insulating effects of the solvent vapors within the vapor zone. Such close placement of the heating coils or source to the parts is not always feasible.